The present invention relates generally to the data processing field, and more particularly, relates to a method and communications apparatus for scheduling communications including both cells and frames over a data communications network.
An Asynchronous Transfer Mode (ATM) network described in xe2x80x9cATM: Theory and Applicationxe2x80x9d by David E. McDysan and Darren L. Spohn, McGraw-Hill, 1994 is an internationally agreed upon technique for transmission, multiplexing and switching in a broadband network. ATM networks are designed to support the integration of high quality voice, video, and high speed data traffic. ATM networks use fixed size cells as a unit of transmission. As technology increases, it is expected that the Asynchronous Transfer Mode (ATM) technology and ATM networks will supply much of the need for high speed network interconnection.
In the face of emerging proprietary optical transmission protocols, SONET (Synchronous Optical Network) was provided as an open standard for synchronous data transmission on optical media. The standard was approved in 1988 by the predecessor to today""s International Telecommunication Union, and in 1989 by the American National Standards Institute. SONET is widely deployed in the US. Using time division multiplexing, SONET works by dividing a fiber transmission path into multiple logical channels called tributaries. A tributary""s basic unit of transmission is an STS-1 (synchronous transport signal, level 1) or OC-1 (optical carrier, level 1) signal. STS describes a transmission""s signals while in an electrical state, and OC describes the same traffic after being converted into optical signals. STS-1 and OC-1 both operate at 51.84 Mbps. OC2 is twice as fast, OC-3 is three times as fast, and so on. SONET is based on direct synchronous multiplexing, where separate signals are multiplexed directly into higher speed signals. For example, an OC-12 circuit might carry traffic from four OC-3 links. SONET line rates are currently operating up to OC-192 (9.953 Gbps). This is considerably faster than ATM""s maximum current rate of 622 Mbps or Ethernet""s current rate of 1 Gbps.
Ethernet is the original and still common name for the communications technique that has been standardized by the IEEE as some of the 802.x standards. 802.3 is the general Ethernet standard and 802.x are the link layer standards covering a variety of speeds.
A Packet over SONET communications interface is described in xe2x80x9cPOS-PHY(trademark) SATURN COMPATIBLE PACKET OVER SONET INTERFACE SPECIFICATION FOR PHYSICAL LAYER DEVICES (Level 2)xe2x80x9d by PMC-Sierra, Inc. Saturn Group, Issue 2, January, 1998. Also, RFC 2171 documents a multiple access protocol for transmission of network-protocol datagrams, encapsulated in High-Level Data Link Control (HDLC) over SONET/SDH (Synchronous Digital Hierarchy).
Asynchronous Transfer Mode or ATM is a communication technology whose use is becoming more widespread in some areas while receiving competitive competition from Gigabit Ethernet and Packet Over SONET (POS) in other areas. The system designer and IS administrator is faced with the daunting task of choosing one technology over another, and allocating scarce development resource to optimize in their individual system one or another of these technologies. If there were a way to isolate the differences of these various technologies from the preparation for the use of the technology, the benefits would be widespread.
A related patent application is copending Ser. No. 09/243858, filed on the same date as the present application, entitled: COMMUNICATIONS ADAPTER FOR IMPLEMENTING COMMUNICATIONS IN A NETWORK AND PROVIDING MULTIPLE MODES OF COMMUNICATIONS, by Branstad et al., and assigned to the present assignee. The subject matter of the above identified patent application is incorporated herein by reference.
A related patent application is copending Ser. No. 09/243956, filed on the same date as the present application, entitled: COMMUNICATIONS METHODS AND GIGABIT ETHERNET COMMUNICATIONS ADAPTER PROVIDING QUALITY OF SERVICE AND RECEIVER CONNECTION SPEED DIFFERENTIATION, by Branstad et al., and assigned to the present assignee. The subject matter of the above identified patent application is incorporated herein by reference.
To this end, a need exists to design and construct communication adapters and networking equipment that provide a simple, efficient, and versatile interface to a system and at the same time be capable of communicating in a variety of modes. A need exists for an improved method and apparatus for scheduling the transmission of both cells and frames in a communications network.
Important objects of the present invention are to provide an improved method and apparatus for scheduling the transmission of cells and frames in a communications network; and to provide such method and apparatus that overcome disadvantages of prior art arrangements.
In brief, a method and apparatus are provided for scheduling the transmission of cells and frames in a communications network. The transmission of cells and frames are scheduled utilizing a selected scheduling algorithm. The cell/frame scheduling algorithm includes the step of identifying a frame or cell transmission type. Responsive to the identified frame or cell transmission type, a frame multiplier value is identified. A target transmission time is calculated for the frame or cell transmission type utilizing the identified frame multiplier value.
In accordance with features of the invention, cells are fixed sized and frames are variable sized. Frames presented for transmission on a cell based interface are segmented into cells and are transmitted, possibly using multiple transmission opportunities. A frame presented for transmission on a frame based interface is transmitted using a single transmission opportunity.
In accordance with features of the invention, a method and apparatus optionally are provided for scheduling the transmission of packet pairs.